1. Field of the Invention
The present invention relates to a roll member and a fusing device using the roll member which are employed in image forming apparatuses such as copying machines and laser beam printers.
2. Description of the Related Art
A fusing device in electrophotographic image forming apparatuses, such as copying machines and laser beam printers, has a pair of rollers for gripping between them a recording material to which a toner image has been transferred, and fixes the toner image onto the recording material to provide a permanent image by applying heat and pressure to a toner. Those rollers for use in the fusing device each have an outer layer formed by coating over its surface a material that is superior in releasability, heat-resistance and wear-resistance, such as fluorocarbon resin or silicone rubber.
In electrophotographic image forming apparatuses for color copying machines in which importance is placed on image quality, particularly, there is a tendency to employ a roller whose surface is covered with silicone rubber. Also, Japanese Patent Laid-Open No. 9-71725 proposes one of such type of rollers in which a silicone rubber layer contains a metal compound to give the roller superior wear-resistance and heat-resistance. Further, Japanese Patent Laid-Open No. 8-328342 proposes a fusing roller in which an inorganic fine powder is added to a silicone rubber layer to improve the physical strength.
With recent widespread use of color printers, the demand for a reduction of the running cost has become increasingly critical. To satisfy such a demand, the amount of oil applied as a releasing agent to the silicone rubber must be reduced. A reduced amount of oil on the rubber surface changes the surface characteristics of the rubber itself and directly affects the operation of a fusing roller in various ways. As a primary effect, when a sheet of recording paper is gripped and transported by a pair of rollers, a frictional force developed between the rubber and the paper is so largely affected that the paper wrinkles depending on the image formed on the paper.
Specifically, a releasing agent is usually applied in a smaller amount to one of the paired rollers which is located opposite to the other roller held in contact with a releasing agent applicator. Depending on the image formed on the surface of the paper contacting the one roller theref 3ore, the paper is subjected to stresses and is forced to wrinkle. In the roller having a surface layer formed of a silicone rubber layer which contains a metal compound, particularly, the metal compound increases viscosity of the silicone rubber layer and then enhances affinity of the silicone rubber layer for oil. The coefficient of friction between a toner area (i.e., an area of the recording paper in which a toner image is formed) and the roller surface is reduced due to the presence of oil between them, while the coefficient of friction between a non-toner area (i.e., an area of the recording paper in which a toner image is not formed) is not so reduced because the non-toner area absorbs oil. Accordingly, the transport speed of the recording paper varies locally, thus causing the paper to wrinkle.
An object of the present invention is to provide a roll member which has wear resistance and is able to prevent a sheet of recording paper from wrinkling, as well as a fusing device employing the roll member.
To achieve the above object, the present invention provides a roll member having, as a surface layer, a silicone rubber layer containing a metal compound MmXn and an inorganic fine powder, wherein M is a cation selected from among ions of Al, Sc, Cr, Fe, Co, Ni, Cu, Zn and Ga, X is an anion selected from among ions of halogens, inorganic acids and organic acids, and m and n are each a positive integer on condition that the valence number of mxc3x97M is equal to the valence number of nxc3x97X.
Also, the present invention provides a fusing device comprising a fusing roller and a pressing roller to transport a recording material, on which a not-yet fused toner is carried, while gripping the recording material between the fusing roller and the pressing roller, thereby fusing the not-yet fused toner onto the recording material, wherein a surface layer of at least one of the fusing roller and the pressing roller is a silicone rubber layer containing a metal compound MmXn and an inorganic fine powder.
The present invention has succeeded in solving the problem of paper wrinkles, which occur due to addition of the metal compound, by adding the inorganic fine powder to the surface silicone rubber layer of the roll member. Such an effect of the inorganic fine powder presumably results from the fact that the coefficient of friction between a non-toner area of the recording paper and the roller surface is reduced by the presence of the inorganic fine powder in the roller surface.
The roll member according to the present invention is employed as the fusing roller, or the pressing roller, or each of the fusing roller and the pressing roller depending on the construction of the fusing device so that the occurrence of paper wrinkles can be effectively avoided.